1. Field of the Invention
This invention relates to an electromagnetic sound generator in which sound is generated by vibrating a vibration plate using an electromagnet. More particularly, the invention relates to an electromagnetic sound generator having such a structure that surface-mounted electrodes and coil connections are disposed in an area in which the magnet is placed.
2. Description of the Related Art
Surface-mounted electromagnetic sound generators of this type in accordance with the prior art have structures of the kind shown in FIGS. 5 to 8. Specifically, the surface-mounted electromagnetic sound generator illustrated in FIGS. 5 and 6 includes a ring-shaped magnet 6 disposed about the periphery of a coil 4 attached to a central yoke 2, and a vibration-plate supporting frame 10, which supports a vibration plate 8, disposed about the periphery of the magnet 6. To connect terminals 4a, 4b of the coil 4, the terminals 4a, 4b are passed beneath the magnet 6 and vibration-plate supporting frame 10, led out to the exterior of the magnet 6 and vibration-plate supporting frame 10 and soldered to connecting portions 12a, 14a of electrodes 12, 14, respectively.
To connect coil terminals in the conventional surface-mounted electromagnetic sound generator depicted in FIGS. 7 and 8, use is made of a planar, generally C-shaped magnet 16 a part which has a cut-out 16a, the connecting portions 12a, 14a of the respective electrodes 12, 14 are led into the cut-out 16a of the magnet 16 and the terminals 4a, 4b of the coil 4 are soldered to the connecting portions 12a, 14a, respectively.
In the conventional surface-mounted electromagnetic sound generator shown in FIGS. 5 and 6, the terminals 4a, 4b of the coil 4 and the connecting portions 12a, 14a of the respective electrodes 12, 14 are connected in a space located outside the magnet 6. This is disadvantageous in that the size of a case 18 must be increased by an amount commensurate with the connection space, thus making it difficult to achieve a more compact design.
In the conventional surface-mounted electromagnetic sound generator shown in FIGS. 7 and 8, the terminals 4a, 4b of the coil 4 and the connecting portions 12a, 14a of the respective electrodes 12, 14 are connected in the cut-out 16a of the magnet 16. This makes it possible to achieve a size that is smaller in comparison with the structure shown in FIG. 5. However, since use is made of the generally C-shaped magnet 16, the cut-out 16a causes a slight imbalance in the characteristics of the magnetic circuit as compared with the ring-shaped magnet. Though this is so small as to have absolutely no effect upon such factors as the frequency characteristic and sound-pressure level, which are important characteristics of an electromagnetic sound generator, it does cause the vibration plate 8 to vibrate abnormally, as by causing the vibration plate to vibrate non-uniformly. This can result in metallic sounds caused by sound break-up. In particular, since it is required that the two terminals of the coil be soldered to two connecting portions of electrodes inside the cut-out 16a, this necessitates enough space to receive the two connection locations and to allow the soldering work. It is difficult, therefore, to reduce the size of the cut-out 16a and, as a consequence, to improve balance of the characteristics of the magnetic circuit.
Accordingly, an object of the present invention is to provide a surface-mounted electromagnetic sound generator in which space for connections between coil terminals and surface-mounted electrode is provided without enlarging the size of the device, and in which performance can be enhanced by eliminating abnormal vibration of the vibration plate.
According to the present invention, the foregoing object is attained by providing a surface-mounted electromagnetic sound generator comprising: a case; a yoke accommodated inside the case; a coil attached to the yoke; a ring-shaped magnet placed about the coil and having an inner circumferential surface, an outer circumferential surface and an underside provided with a plurality of recesses at symmetrical positions thereof, each recess extending through the magnet in tunnel-like fashion from the inner circumferential surface to the outer circumferential surface; a vibration plate disposed to oppose the yoke; and a plurality of surface-mounted electrodes each having a joining portion led out to the exterior of the case for being joined to an external electrically. conductive member, and a connecting portion led into one of the recesses of the magnet; wherein the terminals of the coil are pulled into-the plurality of recesses of the magnet and attached to respective ones of the connecting portions of the electrodes.
According to another aspect of the present invention, the foregoing object is attained by providing a surface-mounted electromagnetic sound generator comprising: a case; a yoke accommodated inside the case; a coil attached to the yoke; a ring-shaped magnet placed about the coil and having an inner circumferential surface, an outer circumferential surface and an underside provided with a plurality of recesses at symmetrical positions thereof, each recess extending into the magnet in tunnel-like fashion from the inner circumferential surface without opening to the outer circumferential surface; a vibration plate disposed to oppose the yoke; and a plurality of surface-mounted electrodes each having a joining portion led out to the exterior of the case for being joined to an external electrically conductive member, and a connecting portion led into one of the recesses of the magnet; wherein the terminals of the coil are pulled into the plurality of recesses of the magnet and attached to respective ones of the connecting portions of the electrodes.
The connecting portions of the plurality of electrodes in the surface-mounted electromagnetic sound generator are either led into respective ones of different recesses of the plurality thereof or into one recess of the plurality thereof.
Thus, in the surface-mounted electromagnetic sound generator according to embodiment of the present invention, the terminals of the coil are connected to the connecting portions of the electrodes in the plurality of recesses provided in the ring-shaped magnet at symmetrical positions. Specifically, the recesses of the magnet are positioned so as to be mutually symmetrical and are formed as openings in the underside of the magnet so as to pass through the magnet from its inner to its outer circumferential surfaces in tunnel-like fashion. The coil is situated inside the magnet and its terminals are pulled into the recesses from the openings on the inner circumferential side and are connected to the respective connecting portions of the electrodes within the recesses. The connections between the coil terminals and the electrode connecting portions, therefore, fall within the space where the magnet is disposed. As a result, the space where the connections are located need not be provided on the outer side of the magnet or vibration-plate supporting frame. This makes it possible to obtain an extremely thin and small-size sound generator.
Further, providing the plurality of recesses at symmetrical positions eliminates local variations in the strength of magnetic lines of force that act upon the vibration plate, thereby providing greater uniformity in the lines of force. This makes it possible to prevent the occurrence of abnormal vibrations in the vibration plate and to improve performance.
Further, the connecting portions of the plurality of electrodes are led into different recesses, with one connecting portion being led into one recess. The terminals of the coil are connected to respective ones of the connecting portions thus led into different respective ones of the recesses. This means that the size of the opening to each recess need only be large enough to accommodate one terminal of the coil and one connecting portion of an electrode. Accordingly, the width of the, opening of each recess can be very small and the balance of the characteristics of the magnetic circuit can be improved.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.